1. Field of the Invention
The present invention relates to the field of in vivo sensors and, in particular, to in vivo sensors that are implanted in non-vascular areas of the body. The present invention also relates to a system and method for accurately measuring a physiological parameter in areas of a body (or external to the body) where amounts of the physiological parameter are heterogeneous in nature.
2. Description of Related Art
Traditional methods of physiological parameter sensing typically rely on vascular placement of a physiological parameter sensor. Such placement permits a sensing element such as, for example, a biomolecule, to make direct contact with the blood, providing sensing capabilities of blood components. Such sensing capabilities have greatly facilitated analysis, diagnosis and treatment of many debilitating diseases and medical conditions.
However, vascular placement of a physiological parameter sensor may suffer from several disadvantages. A physiological parameter sensor is not inserted into a vein without great difficulty and painstaking effort by an attending physician. Moreover, a physiological parameter sensor is not adjusted within or extracted from a vein without similar difficulty and effort.
Furthermore, vascular placement of a physiological parameter sensor subjects the sensor to a constant fluid environment. Such an environment may have several detrimental effects on the sensor. Due to constant fluidic contact, the sensor may suffer from decreased sensitivity, stability and effective life. Should a characteristic of the sensor be diminished to an extent rendering the sensor ineffective, the sensor must be removed and replaced, introducing the difficulties for both patient and physician associated with such removal and replacement. To complicate matters, every time a physiological parameter sensor is removed and replaced, it must be disconnected and reconnected to an implant unit utilizing the sensor output.
In an effort to assuage some of the disadvantages associated with vascular implantation of physiological parameter sensors, integrated sensor/implant unit systems have been developed. Such systems may be placed in or near a body cavity and may provide non-vascular sensing of physiological parameters. However, the incision required for such sensor/implant unit systems is relatively large and the trauma in the area of implantation can be significant. Such trauma generally prevents sensing of physiological parameters. Because such trauma may not subside for several weeks or a month or even longer, pre-implantation analysis methods used by the patient must continue. Without continuation of preimplantation analysis methods, a patient may go undiagnosed and untreated for many weeks, possibly even a month or longer. Such delay in treatment and diagnosis could be harmful or even fatal for patients who need daily diagnosis and treatment.
In addition, vascular implantation of physiological parameter sensors allow the sensing elements to sense a relatively homogenous amount of oxygen or other physiological parameter as it flows past the sensing elements. In contrast, when placing the sensor in a non-vascular area of the body, the physiological parameter may have a more heterogeneous nature, i.e., the amount of the physiological parameter may vary significantly at different locations within the non-vascular area. In such a case, the sensing element may sense the physiological parameter through diffusion from, for example, fluid around the sensing element. Thus, depending on the location of the sensing element within the non-vascular area, the amount of the physiological parameter sensed by the sensing element may more or less accurately represent the “overall amount” of the physiological parameter within the non-vascular area, i.e., an amount that accurately represents, for example, an average amount or other suitable statistical measure of the physiological parameter in the particular area of the body. In addition, another problem results from the fact that the heterogeneous nature of the physiological parameter being sensed by the sensing element may induce noise in the signal obtained from the sensing element.